Reduction in the size of active isolation structures in a semiconductor die, e.g., for locating transistors and/or other circuit elements, has typically been limited by the lithographic processes available. As the size of transistors has decreased and the density of transistors on the semiconductor die has increased due to improvements in lithographic fabrication processes, active isolation structures for locating these transistors have been unable to decrease proportionally in size with the smaller and/or more densely populated transistors.